From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 94B8E309F1C for ; Tue, 6 Jan 2026 08:14:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767687258; cv=none; b=afvsnLi6ZXqf4C9XpP4QZOghKpkT/J1MOlUXH+j0ASiDXeNgf2a5KQmgGD+1qYCVGWv1/djKotIqUWqPbewLRRKg2E8R2FS3Gm1uigP0+y8vbvZ+jfxMG5lX9FGTyEba4jXUKn3Cl0/xnFcCKJ6VDpg5ISvbmIZjzwGNf7PfsTs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767687258; c=relaxed/simple; bh=F4RtnOEqGW5sahZpVUJ3h1wki9Hc/vi9R3ILi+eHVRQ=; h=Message-ID:Date:MIME-Version:Cc:Subject:To:References:From: In-Reply-To:Content-Type; b=tlqri5W+QRUxqCa6REYiJRCrYuIKTt1OY6+50u+7J1eUzzfUj+/4dee0xeQa5vxFkcWF29h61uFrbWtcSXgiSUgUxx9ejfYObdxCGL77laGZg+tsg9pKag1hMQjWhuboAlYiPeixbMvAjGfczRUCcW/bF/MRnHo38FDgYOfrU5k= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=kg6l7a+h; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="kg6l7a+h" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BD1A1C116C6; Tue, 6 Jan 2026 08:14:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1767687258; bh=F4RtnOEqGW5sahZpVUJ3h1wki9Hc/vi9R3ILi+eHVRQ=; h=Date:Cc:Subject:To:References:From:In-Reply-To:From; b=kg6l7a+hf4m0TOQBrtlm+VJbWZeVvICP8OzjJH7J+zs0xRa6aVIwtuno8WYThBkK5 8o94Tp8Wtnc4BD7NoozDUW2kFx2xkViD8dhhPs2/A0lmzMqxi8LHcbMePnt90RV45b s6aWT1kcHSypcXxRQRHVC5WroPAALkT5XPPSrRj1vBS3SCIqqLSQK7Ho+eAoqenTpC onptQVwJK7zBcBXYLrmhW0EcdAtU8My7QbZB7EBkFxp1xsEDkMPTT9W7urhLkMLpPN INEwcWijAAZzs6GhsSbwwjfgJWcYbkjB8R52SIE2Z+zT/WcB/Z8XPp9AYDehL3RDeQ s6hTQRtN8UCEg== Message-ID: Date: Tue, 6 Jan 2026 16:14:21 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Cc: chao@kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org, syzbot+b4444e3c972a7a124187@syzkaller.appspotmail.com Subject: Re: [PATCH v5] f2fs: fix use-after-free in f2fs_write_end_io To: Szymon Wilczek , Jaegeuk Kim References: <20251223162823.23606-1-swilczek.lx@gmail.com> <20251230140850.70778-1-swilczek.lx@gmail.com> Content-Language: en-US From: Chao Yu In-Reply-To: <20251230140850.70778-1-swilczek.lx@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 12/30/2025 10:08 PM, Szymon Wilczek wrote: > Syzbot reported a slab-use-after-free issue in f2fs_write_end_io(): > > BUG: KASAN: slab-use-after-free in f2fs_write_end_io+0x9b9/0xb60 > Read of size 4 at addr ffff88804357d170 by task kworker/u4:4/45 > > The race condition occurs between the filesystem unmount path > (kill_f2fs_super) and the asynchronous I/O completion handler > (f2fs_write_end_io). > > When unmounting, kill_f2fs_super() frees the sbi structure. However, > if the bio completion callback f2fs_write_end_io() is still running > in softirq context, it may access sbi->cp_wait after sbi has been > freed, causing a use-after-free. > > Fix this by calling synchronize_rcu() before kfree(sbi). Since > bio completion callbacks run in softirq context, which is an implicit > RCU read-side critical section, synchronize_rcu() ensures all > in-flight callbacks have completed before we free sbi. > > Reported-by: syzbot+b4444e3c972a7a124187@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=b4444e3c972a7a124187 > Signed-off-by: Szymon Wilczek > --- > v5: Resend as reply to original thread (v4 was mistakenly sent to a new thread). > v4: Removed f2fs_wait_on_all_pages() call as pointed out by Chao Yu that > it accesses sbi->write_io which has already been freed in f2fs_put_super(). > v3: Simplified to minimal fix - only super.c change with synchronize_rcu(), > as pointed out by Chao Yu that data.c changes are not necessary since > synchronize_rcu() alone guarantees sbi won't be freed before callbacks > complete. > v2: Add synchronize_rcu() to wait for softirq bio callbacks to complete. > fs/f2fs/super.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c > index c4c225e09dc4..dfa3c76c6f2a 100644 > --- a/fs/f2fs/super.c > +++ b/fs/f2fs/super.c > @@ -5454,6 +5454,7 @@ static void kill_f2fs_super(struct super_block *sb) > kill_block_super(sb); > /* Release block devices last, after fscrypt_destroy_keyring(). */ > if (sbi) { > + synchronize_rcu(); Can you please add one line comment to describe why we need to call synchronize_rcu() here? Thanks, > destroy_device_list(sbi); > kfree(sbi); > sb->s_fs_info = NULL;